1. Field of the Invention
The present invention relates to IC sockets, test methods using the same and IC socket mounting mechanisms, and more particularly, to an IC socket for testing a semiconductor device (IC) having projection electrodes formed as bumps or the like, a test method using such an IC socket and a mechanism for mounting such an IC socket.
Many of the ICs used recently are constructed to have projection electrodes formed as solder bumps for connection with an external device, for the purpose of reducing the size of a package. For example, a ball grid array (BGA) has such a construction. Demands for high-density, high-speed semiconductor devices having projection electrodes are growing for further reduction in the package size. Associated with this, pitch between electrodes is on a decreasing trend; and projection electrodes are being arranged with an increasingly higher density and on an increasingly reduced scale.
Once produced, the ICs are subject to a performance test to see if a prescribed performance is provided. The ICs are tested by being mounted on an IC socket. Therefore, the IC socket should be adapted for the high-density, small-scale trend of the ICs. As a result of the high-density, small-scale trend, the strength of each projection electrode has become extremely low so that it is necessary to ensure that the projection electrodes are not damaged when brought into contact with contact pins provided in the IC socket.
2. Description of the Related Art
FIGS. 1-5 show a construction of a conventional IC socket 1. As shown in FIGS. 1-3, the IC socket 1 generally comprises a socket body 2, a lid 3, contact pins 4 and a substrate 5. The IC socket 1 is designed so that an IC 7 of a BGA type provided with solder bumps 6 (projection electrodes) is mounted on the IC socket 1 and tested for its performance.
The socket body 2 includes a cavity 8 in which the substrate 5 is fitted. The cavity 8 is provided with through holes 9 aligned with the solder bumps 6 formed in the IC 7. The substrate 5 is provided with mounting holes 10 also aligned with the solder bumps 6 formed in the IC 7.
The contact pins 4 are formed by punching a thin metal plate so as to have a crooked configuration that provides a spring action as shown in FIGS. 2 and 3. The contact pins 4 have contact parts 4a, formed at the upper end thereof, inserted into mounting holes 10 of the substrate 5. Terminal parts 4b formed at the lower end the contact pins 4 are inserted into the through holes 9 formed in the cavity 8 and are made to project from the bottom of the socket body 2. The same number of the crooked contact pins 4 is provided as the number of solder bumps 6 formed in the IC 7. The contact pins 4 are designed to remain press-fitted into the through holes 9 and the mounting holes 10 while being accommodated in the IC socket 1.
The lid 3 is rotatably fitted to the socket body 2 by a pivot part 11. By closing the lid 3 when the IC 7 has been mounted on the socket body 2, the lid 3 presses the IC 7 toward the substrate 5. As a result, the bumps 6 formed in the IC 7 are pressed against the contact parts 4a of the contact pins 4. The contact pins 4 are elastically deformed so as to press the solder bumps 6 by the elastic action. Accordingly, the contact pins 4 and the solder bumps 6 are electrically connected. A lock lever 12 is provided in a lid 3. The lock lever 12 locks the lid 3 in the closed position.
The IC socket 1 having the above-described construction is designed to be mounted on a test board 13 by a solder reflow process or the like after the terminal parts 4b projecting from the underside of the socket body 2 are inserted into through holes 14 formed in the test board 13. The test board 13 is connected to a test device (for example, a burn-in test device) for performing a test of the IC 7. Thus, a prescribed test is performed on the IC 7 mounted on the IC socket 1 via the test board 13.
It is known that a thin oxide film 15 (see FIG. 5) is formed on the surface of the solder bumps 6 formed in the IC 7. Since the oxide film 15 has a low conductivity, it is necessary to penetrate the oxide film 15 in order to establish an electrical connection between the solder bumps 6 and the contact pins 4.
Conventionally, as shown in FIG. 4 showing the part A indicated by the arrow in FIG. 3 on an enlarged scale, the elastic deformation of the contact pins 4 occurring when the lid 3 is closed is utilized. More specifically, it is expected that the elastic deformation causes the contact parts 4a of the contact pins 4 to be displaced in the direction indicated by the arrow of FIG. 4 so that the contact parts 4a slide on the surface of the solder bumps 6 such that the contact parts 4a penetrate the oxide film 15.
With the increasingly smaller solder bumps 6 provided on the IC 7 recently, the strength of the solder bumps 6 has decreased. Accordingly, the method whereby the contact parts 4a are expected to penetrate the oxide film 15 by sliding on the surface of the solder bumps 6 produces a deformation in the solder bump 6 while the contact parts 4a slide on the surface thereof. The deformation of the solder bumps is indicated by the arrow 6a of FIG. 5. If any of the solder bumps 6 is deformed, a variation in the height of the solder bumps 6 occurs when the IC 7 is mounted on a circuit board or the like after the test. The solder bumps 6 may not be properly mounted on the circuit board.
In the conventional IC socket 1, a high level of precision is required to provide the contact pins 4 having a crooked configuration that provides a spring action in the socket body 2. The press-fitting of the crooked contact pins 4 demands intensive attention. Another problems is that, as the size of the contact pins 4 become smaller with the reduction in the size of the solder bumps 6, it is increasingly difficult to produce the contact pins 4 having a complex crooked configuration, and the cost of the production increases accordingly.